As European capitals go, Berlin is not very old. But it is more laden - or burdened - with history than most, especially with "recent history," as the Nazi period, from 1933 to 1945, is delicately referred to in Germany.

What is the appropriate architectural expression of a people's efforts to come to terms with their dark past?

That is the question running through "The Ghosts of Berlin." Brian Ladd's book is an architectural history of a sort and would be a useful guide for travelers of the armchair variety. But Ladd's focus is less on the aesthetics of buildings and other structures than on their role as repositories of memory: The Wall, and the no man's land alongside it; Potsdamer Platz, once famously "the busiest intersection in Europe" but after the war an utter wasteland, now transformed again into Europe's biggest construction site.

More troubling are the questions of Hitler's infamous bunker at the center of the city and the Gestapo headquarters. How should these sites be preserved? Or should they be preserved at all? And how should Berlin memorialize the victims of the Holocaust?

One of the most interesting sections of the book considers the Reichstag building, the home of and therefore symbol of the "semi-parliamentary" democracy under the Kaisers (1871-1918). He recounts the Bulgarian-born American artist Christo's 20-year campaign for permission to "wrap" the building. It took an act of parliament, literally - the vote was 292 to 223 - but permission was finally granted, and the wrapping proceeded in June 1995, shortly before work began on a major renovation of the building as the future home of the Bundestag, or parliament.

Christo had important supporters among political conservatives. "This was art, after all, and educated Germans tend to take art, even whimsical art, very seriously, and to associate it with dignity," Ladd writes.

It has proved difficult enough for Germany to honor the victims of Nazism. It has proved even more difficult to confront the history of the perpetrators. "The concentration of troubling memories, physical destruction, and renewal has made Berliners, however reluctantly, international leaders in exploring the links between urban form, historical preservation, and national identity," he writes.

Nowadays Berlin is in the midst of a (re)building boom as the government prepares to move back from the "provisional capital" in Bonn; this makes the questions Ladd raises almost painfully topical.

In one sense the decision to move was inevitable: For years, the dream of a reunified Berlin as capital of a reunified Germany was a sacred flame kept alive during the cold war. But now that reunification is a fact, the political leadership is having to tread carefully. Any construction program that seems too grand is going to evoke critics' charges of "imperial delusions."